4 Answers
4

That all depends on the application that is using the registry key. When a key is updated, it is updated, but an application my only look at the key at startup. Rebooting is just a simple way of ensuring that the new key is loaded.

This value enables Windows Vista to
share network connections between the
filtered access token and the full
administrator access token for a
member of the Administrators group.
After you configure this registry
value, LSA checks whether there is
another access token that is
associated with the current user
session if a network resource is
mapped to an access token. If LSA
determines that there is a linked
access token, it adds the network
share to the linked location.

The key itself is updated and valid in the registry as soon as you modify it, like headyd said. However, this will most likely be read by the system only at logon time, so you will have to reboot, or at least log again.

Registry is like a database of parameters available for programs. But it's only a place to read and store parameters, it won't trigger an update in the concerned programs when you change a value.

I just wonder if you can identify a service that integrates with the registry setting, and just restart that service. A wild guess, would restarting the workstation or server service circumvent a reboot? Else any of those services beginning with Microsoft or Windows.